Muscle Tissue Muscle Tissue Gen. Info. Muscle tissue makes up - PowerPoint PPT Presentation

Muscle Tissue

Muscle Tissue – Gen. Info. • Muscle tissue makes up nearly half the body’s mass, with over 700 different skeletal muscles! • The main tissue in the heart and walls of hollow organs • The terms sarco… and mys… come from greek words meaning “flesh” & “muscle”. 2

Overview of Muscle Tissue I. Functions of muscle tissue 1. Movement A. Skeletal muscle ‐ attached to skeleton creates movements of the body (joints & leverage systems) B. Smooth muscle – squeezes fluids and other substances through hollow organs C. Regulates entrance and exit of materials into, through & out of body 2. Maintenance of posture 3. Joint stabilization 4. Thermogenesis 5. Support & Protection of soft tissues/organs 3

Overview of Muscle Tissue II. Characteristics of Muscle Tissue 1. Contractility 2. Excitability 3. Extensibility 4. Elasticity 4

Overview of Muscle Tissue III. Types of Muscle Tissue 1. Skeletal muscle tissue – packaged into skeletal muscles (700+) A. Makes up 40% of body weight 2. Cardiac muscle tissue 3. Smooth muscle tissue – occupies the walls of hollow organs 5

Muscle Comparison Chart Muscle Special Striae Tissue Cell Shape Nucleus structures Control Multi- Skeletal Cylindrical Yes Voluntary none nucleate & peripheral Intercalated Uninucleate Cylindrical Cardiac Yes Involuntary discs & central & branched May be Uninucleate Involuntary No Fusiform Smooth single-unit & central or multi-unit 6

Commonalities of Muscle Tissue • Cells of skeletal and smooth muscles are known as muscle fibers • Muscle contraction depends on two types of myofilaments – One type contains globular actin and other proteins – Another type contains myosin • It is the action of myosin on actin that allows these two proteins to generate contractile force – Muscle contraction occurs along its longitudinal axis only • Plasma membrane is called a sarcolemma • Cytoplasm is called sarcoplasm 7

Skeletal Muscle • Each muscle is an organ that . . . – Consists mostly of muscle tissue – but also contains – Connective tissue – strong attachments continuous through muscle structure – Blood vessels – nourishment & waste removal – Nerves – communication & control 8

Basic Features of a Skeletal Muscle I. Connective tissue and fascicles A. Connective tissue sheaths bind a skeletal muscle and its fibers together Epimysium – dense regular 1. connective tissue surrounding entire muscle 2. Perimysium – surrounds each fascicle (group of muscle fibers) Endomysium – a fine sheath of 3. connective tissue wrapping each muscle cell B. Connective tissue sheaths are continuous with tendons 9

Basic Features of a Skeletal Muscle Line view of the relationship between the connective tissue coverings. Muscle fiber endomysium muscle bundle fascicle All the fibrous sheaths are perimysium epimysium continuous to the tendon! - why? Where is the contractile event? Where is the force applied? 10

Basic Features of a Skeletal Muscle II. Innervation & Vasculature A. Each skeletal muscle has innervations and vasculature which becomes an integral portion of the muscle B. The motor unit consists of the muscle fibers, blood vessels and the nerve that innervates it. 1. Nerves a. Efferent Motor nerves enter the muscle and divide continually until each motor unit has innervation, the neuromuscular junction . b. Afferent sensory nerves provide feedback about muscle tension 2. Arteries & Veins a. Arteries enter and divide continually until each muscle fiber has a capillary network around it to provide the muscle with oxygen, nutrients and provide a route for removal of waste (carbon dioxide, heat, lactic acid. . .) 11

Basic Features of a Skeletal Muscle III. Muscle attachments A. Most skeletal muscles run from one bone to another, or possibly span across more than one bone (biarticular muscle ex. flexor carpi radialis) B. One bone will move – other bone remains fixed or stable 1. Insertion – more movable attachment 2. Origin – less movable attachment 12

Basic Features of a Skeletal Muscle III. Muscle attachments (continued) C. Muscles attach to origins and insertions by connective tissue 1. Fleshy attachments – connective tissue fibers are short 1. Ex. pectoralis major . . On the origin side 2. Indirect attachments – connective tissue forms a tendon or aponeurosis 1. Visible anytime a longer “cord” is present, or a broad flat sheet. 3. Skin, cartilage, sheets of fascia or raphe (line/ridge of a ligament) D. Bone markings present where tendons meet bones 1. Tubercles, trochanters, tuberosities, crests… any roughened surface 13

Microscopic and Functional Anatomy of Skeletal Muscle Tissue I. The skeletal muscle fiber A. Fibers are long and cylindrical 1. Are huge cells – diameter is 10 ‐ 100µm 2. Length – several centimeters to dozens of centimeters B. Each cell formed by fusion of many embryonic cells C. Cells are multinucleate (due to above) D. Nuclei are peripherally located 1. Due to the majority of the cell’s internal space taken up by the myofilaments. E. Cell membrane is called the sarcolemma 14

Microscopic and Functional Anatomy of Skeletal Muscle Tissue F. Striations result from internal structure of myofibrils G. Myofibrils – long rods within cytoplasm 1. Make up 80% of the cytoplasm 2. These contain the smallest contractile units of a muscle in repeating segments called sarcomeres. 15

Diagram of Part of a Muscle Fiber 16 Figure 10.4b

Important Components We Will Consider • The neuromuscular junction (NMJ) • The sarcolemma • The t ‐ tubules and sarcoplasmic reticulum (SR) • The sarcomere it’s filaments • The structural aspect of muscle contraction 17

The NMJ, Sarcolemma, T Tubules & SR I. What is it’s role in muscle contraction? A. Action potential is transferred to the sarcolemma at the neuromuscular junction B. Impulse travels along the sarcolemma of the muscle cell (multidirectionally) 1. Impulses further conducted by t tubules a. T tubule – a deep invagination of the sarcolemma b. The close proximity of the t tubules to the sarcoplasmic reticulum causes it (SR) to depolarize, opening Ca gated channels, allowing Ca to diffuse rapidly out of the SR. 18

The NMJ, Sarcolemma, T Tubules & SR • Sarcoplasmic reticulum is specialized smooth ER – Interconnecting tubules surround each myofibril • Some tubules form cross ‐ channels called terminal cisternae • Cisternae occur in pairs on either side of a t tubule – Contains calcium ions • released when muscle is stimulated to contract after the events at the neuromuscular junction – Calcium ions diffuse through cytoplasm • Trigger the sliding filament mechanism – bind to troponin. . . at the sarcomere level.. 19

Sarcomere • The basic unit of contraction of skeletal muscle – Z disc (Z line) – boundaries of each sarcomere – Thin (actin) filaments – extend from Z disc toward the center of the sarcomere – Thick (myosin) filaments – located in the center of the sarcomere • Overlap inner ends of the thin filaments • Contain ATPase enzymes 20

Sarcomere Structure • A bands – full length of the thick filament – Includes inner end of thin filaments • H zone – center part of A band where no thin filaments occur • M line – in center of H zone – Contains tiny rods that hold thick filaments together • I band – region with only thin filaments – Lies within two adjacent sarcomeres 21

Sarcomere and Myofibrils 22

Sliding Filament Structures 23 Figure 10.6a

Changes in Striation During Contraction 24

Microscopic and Functional Anatomy of Skeletal Muscle Tissue • Muscle extension – Muscle is stretched by a movement opposite that which contracts it • Muscle fiber length and force of contraction – Greatest force produced when a fiber starts out slightly stretched – Myosin heads can pull along the entire length of the thin filaments 25

The Role of Titin • Titin – a spring ‐ like molecule in sarcomeres – Resists overstretching – Holds thick filaments in place – Unfolds when muscle is stretched 26

Neuromuscular Junction 27

Sarcoplasmic Reticulum and T Tubules in the Skeletal Muscle Fiber 28

Sarcoplasmic reticulum network and terminal cisternae 29

Types of Skeletal Muscle Fibers • Skeletal muscle fibers are categorized according to: – How they manufacture energy (ATP) – How quickly they contract • Skeletal muscle fibers are divided into three classes: – Slow oxidative fibers (Type I) – Fast oxidative fibers (Type IIa) – Fast glycolytic fibers (Type IIx) – Fast glycolytic fibers (Type IIb) 30